1. Field of the Invention
The present invention relates to apparatuses for controlling a quantity of fuel to be actually sprayed from an injector of an internal combustion engine operating in multiple injection mode. In the multiple injection mode, the internal combustion engine causes the injector to carry out multiple shots of fuel in one operating cycle of the internal combustion engine.
2. Description of the Related Art
Fuel injection systems are commonly used to control fuel injection by an injector for each cylinder of an internal combustion engine. In order to reduce combustion noise, nitrogen oxides (NOx) emissions, and/or regeneration of an exhaust gas filter, one type of the fuel injection systems is designed to cause an injector to carry out, in a multiple injection mode (multistage injection mode), multiple shots of fuel in one operating cycle of the internal combustion engine.
The injector is normally designed to move a valve to open a port to thereby spray a quantity of fuel into a corresponding cylinder, and move the valve to close the port to thereby stop the spray of fuel thereinto.
In the multiple injection mode, the fuel injection system of the one type is designed to cause an injector to spray a small quantity of fuel into the engine before and after a main shot (main injection) of fuel. The main injection of fuel allows the engine to generate torque. The injection prior to the main injection of fuel win be referred to as “pilot injection” hereinafter, and the injection after the main injection will be referred to as “post injection”.
In the multiple injection mode, water hammer occurs in the injector at the moment when the valve closes the port of the injector to stop the shot of fuel in each stage injection, resulting in pressure pulsations in the injector. The pressure pulsations cause influence on valve open/close timing of the injector. The magnitude of the pressure pulsations depends on an elapsed time since the stop of the shot of fuel in each injection stage.
For this reason, when the pressure pulsations occur in the injector in a former injection, the quantity of fuel sprayed from the injector in a latter injection following the former injection varies depending on an interval period. The interval period is defined as an interval period from the stop of the spray of fuel in a former injection to the start of spraying fuel in a latter injection following the former injection. For the sake of simplification, the interval period can be described as “interval period between former and latter injections” and the like hereinafter.
The variations in the quantity of fuel sprayed from an injector may reduce the accuracy in controlling the quantity of fuel to be sprayed from an injector.
Thus, a method for addressing such an accuracy reduction problem has been proposed. The method includes, at the time of shipment of a fuel injection system or the like, the steps of:
measuring a characteristic indicative of the relationship between interval period and pressure pulsation for each injector; and
determining reference I-Q characteristic data in, for example, map format based on the measured characteristic.
The reference I-Q characteristic data represents a reference relationship between target interval period from a former injection by an injector to a latter injection following the former injection and correction value of a quantity of fuel actually or sprayed from the injector in the latter injection.
Specifically, when a target interval period between a former injection and a latter injection carried out by an injector in the multiple injection mode is set, it is possible to reference the reference I-Q characteristic data to retrieve a correction value corresponding to the set target interval period. Thus, an instruction value corresponding to the target injection quantity for the latter injection is corrected based on the correction value, and thereafter, the corrected instruction value is outputted to the injector. This allows a quantity of fuel actual sprayed from the injector to be matched with the target quantity of fuel for the latter injection.
However, fuel spray characteristics of injectors vary depending on their individual variations (fabrication variations) and an aging of each injector. For this reason, an actual interval period between temporally adjacent fuel injections and a target interval period therebetween are different from each other.
This results in that, even if a target quantity of fuel to be sprayed from an injector in a latter injection is corrected based on a target interval period between a former injection and the latter injection, a quantity of fuel actually sprayed from the injector in the latter injection is deviated from the target quantity of fuel. The target quantity of fuel to be sprayed from an injector will be also referred to as “target injection quantity” hereinafter.
In order to address such a problem, a fuel injection system is disclosed in EP Patent Application Publication No. EP 1775454 corresponding to Japanese Patent Application Publication No. 2007-132334; these patent applications have been filed by the same applicant as this application.
The fuel injection system disclosed in the EP Patent is configured to, in a learning mode, instruct an injector to spray a target quantity of fuel in a first injection, and after a value of a target interval period has elapsed since the stop of the spray of fuel in the first injection, the injector to spray a target quantity of fuel in a second injection. The value of the target interval period is within one of divided sections of a total temporal range usable for the target interval period.
The fuel injection system is also configured to estimate a quantity of fuel actually sprayed from the injector in the second injection, and calculate a difference between the target quantity of fuel and the estimated quantity of fuel actually sprayed therefrom by the second injection.
Thus, the fuel injection system is configured to learn a deviation of an actual interval period from the value of the target injection period based on the calculated difference. The actual interval period is an interval period that has actually elapsed from the stop of the spray of fuel by the injector in the first injection to the start of spraying fuel by the injector in the second injection.
The learned deviation allows, in the multiple injection mode, correction of the reference I-Q characteristic data to match a quantity of fuel actually sprayed from the injector by the second injection with the target quantity of fuel.